The machining of a part from raw stock or material, such as metal, is a form of subtractive manufacturing during which the raw material is progressively removed until the part reaches an intended shape and size. Operations during machining primarily involve turning, drilling and milling the raw material into the desired part, which respectively require removing the raw material by rotating the raw material against a stationary cutting tool, axially boring holes using a rotating bit with a cutting edge on a distal end whilst the raw material is held stationary, and cutting away the raw material using a rotating bit with cutting edges generally along the rotating bit's sides and distal end. Both drilling and milling involve traversing a rotating bit along a longitudinal axis in the Z-direction. Milling, which operates in three-dimensional space, also involves moving the rotating bit along a plane in X- and Y-directions. Other kinds of machining operations and tools also exist. The machining will generally reduce the raw material into rough form within a specified tolerance; further manufacturing processes may be required to smooth, polish, finish, or otherwise transform the part into final form; to check the, such as through inspection or testing; or to assemble a final product.
During manufacture, a part must be immovably mounted using fixtures in suitable configurations that both ensure placement of the part in a known and expected orientation and enable meeting specified manufacturing tolerances. A fixture is a work-holding device that is used to locate and clamp a part's surface to support manufacturing operations, such as machining, inspection and assembly. Typical parts manufacturing requires planning several different fixture layouts or configurations to effectively immobilize the part under manufacture while operated on in various orientations throughout a sequence of manufacturing steps.
The emergence of flexible manufacturing systems has necessitated the design and use of fixtures that have in-built flexibility to rapidly respond to part design changes. These fixtures, known as modular fixtures, represent the most widely-used class of flexible fixtures and are adaptable to a large class of parts. While the design and fabrication of fixtures may reach 20% of the total manufacturing cost, the use of flexible or reconfigurable fixtures can reduce fixture costs by as much as 80%. Modular fixtures are often used for moderate or small manufacturing lot sizes, especially when the cost of dedicated fixtures and the time required to produce the fixtures may be difficult to justify.
Complex work pieces can be located during manufacturing using modular fixtures produced quickly from standard components, and the modular fixtures can later be disassembled for reuse in other parts manufacturing. FIG. 1 is a diagram showing, by way of example, a prior art set of components of a modular fixture 10. Modular fixtures are typically supported on base plates 14 with grid holes or attachment points 15 upon which fixture elements 11, which can include clamps, risers or other components, possibly in combination, are constructed. A fixture element 11 may have a face 12 which will be in contact with a contact location on the part and a mounting feature 12 in contact with an attachment point 15 on the base plate 14. Other fixture element features are possible. Often, details specific to an individual component used in assembling a modular fixture is specialized to a particular purpose and can be unique for each type of component. Increasingly, manufacturers of modular fixture components have listed available components in libraries or catalogs to facilitate manufacturability analysis. For instance, fixture catalogs available online, such as Fixtureworks (www.fixtureworks.net), operated by Fixtureworks, LLC, Fraser, Mich., and Carr Lane (www.carrlane.com), operated by Carr Lane Manufacturing Co., St. Louis, Mo., have devised fixture ontologies for efficiently searching through modular fixture component details in a user-driven query and filter format. In addition, D. Vukelic et al., “A Rule-Based System for Fixture Design,” Sci. Research and Essays, Vol. 6(27), pp. 5787-5802 (2011), the disclosure of which is incorporated by reference, describes a representation for fixture catalogs that applies case-based reasoning methods to fixture planning, and is designed to be compatible with generic geometric reasoning-based algorithms for fixture selection and shop-specific reasoning.
Notwithstanding such searchable component libraries, key challenges remain. One challenge is in determining where on a part under manufacture to contact clamps, such that contact locations are both reachable by the clamps throughout the machining process, yet situated so as to not cause the clamps to interfere with the access paths of tools operating on or around the part. A related challenge is in synthesizing configurations of fixtures that may be used to effectively clamp a specific work piece in place without the clamps overlapping with each other, as well as ideally minimizing the types of clamps needed and the swapping out of different clamp types during a sequence of manufacturing steps.
Fixture configuration and planning continues to be an experience-driven and primarily manual activity, and automated solutions to fixture synthesis do not scale well in accommodating variations in work piece geometry. Fixture configuration and planning focuses on determining precise location and clamping of work pieces according to a part's design and process requirements. Process constraints non-exclusively include collision avoidance with surrounding tooling and expected tool paths, accessibility analysis, deformation considerations, material properties, available fixture elements, and manufacturing tolerances. Conventional approaches for computer-assisted fixture planning, such as described in X. Kang et al., “Recent Research on Computer-Aided Fixture Planning,” Recent Patents on Mechanical Engr., Vol. 2, pp. 8-18 (2009); and K. Lakshminarayana, Mechanics of Form Closure, Springer-Verlag (1978), the disclosures of which are incorporated by reference, address other types of process constraints, and fail to adequately remedy the problem of contact location selection and manufacturing parts fixturing with components from a vendor-supplied catalog.
Therefore, a need remains for an approach to rapidly synthesizing a realistic fixture configuration, including spatial location of clamps or other fixture elements in contact with a work part that will substantially guarantee stability and immobility of a specified work part.
A further need remains for an approach to matching suitable fixtures selected from a fixture components library that ensures effective fixturing and preferably facilitates efficient performance of sequence step s during execution of manufacturing processes.